Instruction Syntax

Mnemonic	Format	Flags
mfcr	rD	None

Instruction Encoding

Field	Bits	Description
Primary Opcode	0-5	011111 (0x1F)
rD	6-10	Destination register
Reserved	11-20	Should be zero
XO	21-30	0x0A2 (162) - Extended opcode
Reserved	31	Should be zero

Operation

rD ← CR

The entire contents of the Condition Register (CR) are copied to general-purpose register rD. The CR contains 32 bits representing all 8 condition register fields (CR0-CR7), each containing 4 bits (LT, GT, EQ, SO).

Note: This instruction provides a way to save the complete state of all condition register fields. This is particularly useful for context switching, interrupt handling, or when complex conditional logic requires preserving all condition codes.

Affected Registers

General Purpose Register

(always)

• rD - Loaded with complete Condition Register contents

Condition Register (CR)

(read only)

• CR - Source register (read only)

For more information on condition codes see Section 2.1.3, "Condition Register," in the PowerPC Microprocessor Family: The Programming Environments manual.

Examples

Basic Condition Register Save

# Save complete condition register state
mfcr r3                 # Copy CR to r3
# ... perform operations that might modify CR ...
mtcrf 0xFF, r3         # Restore CR from r3

Context Switching

# Save context before function call
mfcr r10                # Save condition register
# ... save other registers ...

bl some_function        # Function call

# Restore context after function call
mtcrf 0xFF, r10        # Restore condition register
# ... restore other registers ...

Interrupt Handler

# Interrupt handler entry
interrupt_handler:
    mfcr r20            # Save condition register
    # ... handle interrupt ...
    mtcrf 0xFF, r20    # Restore condition register
    rfi                 # Return from interrupt

Complex Conditional Logic

# Save condition codes for complex logic
cmpwi cr0, r3, 0       # First comparison
cmpwi cr1, r4, 10      # Second comparison
cmpwi cr2, r5, 20      # Third comparison
mfcr r6                # Save all condition codes

# Perform operations that might modify CR
add r3, r3, r4
sub r5, r5, r6

# Restore and use saved condition codes
mtcrf 0xFF, r6         # Restore all condition codes
bt cr0, first_true     # Use first comparison result
bt cr1, second_true    # Use second comparison result
bt cr2, third_true     # Use third comparison result

Nested Function Calls

# Preserve condition codes across nested calls
cmpwi cr0, r3, 0       # Set up condition codes
mfcr r7                # Save them

bl outer_function      # Outer function call
# Outer function might call inner function
# Inner function might modify CR

mtcrf 0xFF, r7         # Restore original condition codes
beq cr0, original_zero # Use original comparison result

Multiple Condition Tracking

# Track multiple conditions simultaneously
cmpwi cr0, r3, 0       # Check zero
cmpwi cr1, r4, 100     # Check range
cmpwi cr2, r5, -50     # Check negative
cmpwi cr3, r6, 200     # Check upper bound
mfcr r8                # Save all conditions

# Process data (might modify CR)
process_data:
    # ... data processing ...

# Check all original conditions
mtcrf 0xFF, r8         # Restore all conditions
bt cr0, was_zero       # Handle zero case
bt cr1, in_range       # Handle range case
bt cr2, was_negative   # Handle negative case
bt cr3, was_large      # Handle large value case

Error Condition Preservation

# Preserve error conditions across operations
cmpwi cr0, r3, -1      # Check for error -1
cmpwi cr1, r4, -2      # Check for error -2
cmpwi cr2, r5, -3      # Check for error -3
mfcr r9                # Save error conditions

# Perform recovery operations
bl recovery_function   # Might modify CR

# Check original error conditions
mtcrf 0xFF, r9         # Restore error conditions
beq cr0, handle_error1 # Handle error -1
beq cr1, handle_error2 # Handle error -2
beq cr2, handle_error3 # Handle error -3

Loop Condition Preservation

# Preserve loop conditions for nested logic
loop_start:
    cmpwi cr0, r4, 0   # Check loop condition
    mfcr r10           # Save loop condition
    
    # Nested operations that might modify CR
    cmpwi cr0, r5, 10  # Some other comparison
    bt cr0, do_something
    
    # Restore loop condition
    mtcrf 0xFF, r10    # Restore original conditions
    beq cr0, loop_end  # Exit if loop condition false
    b loop_start       # Continue loop

Status Flag Management

# Manage multiple status flags
cmpwi cr0, r3, 0       # Zero flag
cmpwi cr1, r4, 0       # Overflow flag
cmpwi cr2, r5, 0       # Error flag
cmpwi cr3, r6, 0       # Ready flag
mfcr r11               # Save all status flags

# Perform system operations
bl system_operation    # Might modify CR

# Check all status conditions
mtcrf 0xFF, r11        # Restore status flags
bt cr0, zero_detected  # Handle zero condition
bt cr1, overflow_detected # Handle overflow
bt cr2, error_detected # Handle error
bt cr3, ready_detected # Handle ready condition

Debugging Support

# Save condition register for debugging
debug_point:
    mfcr r12            # Save CR for debugging
    # ... perform operations ...
    
    # Debug: check if conditions changed unexpectedly
    mfcr r13            # Get current CR
    cmpw r12, r13       # Compare saved vs current
    beq conditions_ok   # Branch if unchanged
    # Handle unexpected condition change

Related Instructions

mcrf, mtcrf, mcrfs, mcrxr